The specific aims of this research proposal are: 1) to investigate the relative potency of cardiac receptors and sinoaortic baroreceptors (and their possible interaction) in mediating vasopressin secretion. Pressures in the receptor areas will be altered by partial occlusion of selected vessels of sham-operated dogs. The relative potency of cardiac receptors and sinoaortic receptors will be obtained by performing similar pressure manipulations in dogs with surgical denervation of one or both of the receptor areas. 2) to study the "direct" and indirect" effects on vasopressin secretion elicited by intravenous administration of angiotensin II, morphine, and histamine. This will be accomplished by measureing plasma vasopressin before and after the administration of these agents to animals that are unable to respond reflexly to the vasoactive properties of these agents because of previous surgical denervation of cardiac and/or sinoaortic baroreceptors. This approach should also provide information regarding the direct effect of these agents on vasopressin secretion by accessing the results form combined sinoaortic and cardiac denervation, and 3) to determine the possible contribution of ventricular receptors to the augmented secretion of vasopressin that occurs in response to hemorrhage by comparing the magnitude of increase in plasma vasopressin during graded hemorrhage in dogs with surgical denervation of the ventricles with data obtained from similar experiments in sham-operated control dogs and in dogs with complete cardiac denervation. All experiments will be performed on trained conscious dogs. These studies are health related because derangements of vasopressin secretion are associated with fluid and electrolyte disturbance. Abnormalities in the regulation of vasopressin may also lead to the development of some forms of hypertension.